Since data communication traffic increases dramatically, Resilient Packet Ring systems (RPR), a new Media Access Control layer technology (MAC), is being standardized by the IEEE 802.17 standard working group. Resilient packet ring system takes best of both SDH/SONET and Ethernet technologies so as to provide a system operating over ring topologies that employs spatial reuse to maximize bandwidth utilization, provides a distributed fairness algorithm, and ensures high-speed traffic protection. It allows full ring bandwidth to be utilized under normal conditions and protects traffic in the case of node or fiber failures while presenting advantages of low cost equipment, high bandwidth granularity, and statistical multiplexing capability.
Resilient Packet Ring systems are developed as a highly resilient data transport network using two counterrotating fiber rings with automatic protection switching of priority data between these rings if a ring segment is unreachable through a local failure on one of the rings. The emphasis for RPR systems is on very high reliability fulfilling the requirement that each sub-network is operational at least 99.999% of total time. This is achievable only with protection switching and plug & play redundancy of key network components. The protection switching is very similar to that of SDH/SONET networks. However, while a SDH/SONET network uses only one of the two rings for normal operation and restricts the second ring to automatic protection switching only, an RPR network uses both rings already in normal operation. Another important difference between SDH/SONET and RPR networks is that RPR networks directly operate with IP packets over fiber at each node in the ring while SDH/SONET networks operate with virtual containers containing IP packets and only source and destination node map or extract the IP packets (or other data formats) in/out of the virtual containers.
RPR networks are planned to reuse SDH/SONET and Ethernet devices of physical layer (referred herein below to as PHY devices). Hence, RPR is considered to work in the MAC layer on top of the physical layer. Accordingly, an RPR system may forward RPR frames to or receive RPR frames from an SDH/SONET or Ethernet framer. RPR systems are planned as local area networks (LAN), metropolitan area networks (MAN), and wide area networks (WAN) with data rates in the rings ranging to 40 Gb/s and higher.
Many present SDH/SONET networks offer capacities of 40 Gb/s or higher in form of multiple 10 Gb/s or even 2.5 Gb/s rings. Offering high data rates through the use of multiple wavelengths each carrying a fragment of the aggregate data rate opens a way to offer high data rates unachievable by other means or before achievable by future optical technologies or simply in a more cost efficient way. In many cases such networks evolved because it was easier to upgrade the aggregate data rate of existing networks by adding additional rings (wavelengths) to the system than by upgrading every node in the system to a higher single wavelength data rate. There are even SDH/SONET framers which exploit this fact by handling multiple SDH/SONET ports in parallel. As illustrated on FIG. 1, designing an RPR system on top of a multi-ring network in the usual way would require the use of many parallel RPR add/drop devices 102-1 to 102-n supporting plug & play redundancy, one per ring 100-1 to 100-n, plus an additional data aggregation device 104, also supporting plug & play redundancy, for the traffic going from the multi-ring network to the link layer interface, e.g. switch or router device 106, a very costly implementation.